Impulse generator



p 2, 1959 H. SCHOLL 3,464,396

IMPULSE GENERATOR Filed Aug. 17, 1967 2 Sheets-Sheet l INTER/VAL COMBUS77011 5N6 [NE INVENTOR Hermann SCHOLL ll fc lh rx'i! v his ATTORNEYSept. 2, 1969 H. SCHOLL IMPULSE GENERATOR 2 Sheets-Sheet 2 Filed Aug.17, 1967 llllluvlllll INVENTOR Hermann SCHOLL his ATTORN :6

3,464,396 IMPULSE GENERATOR Hermann Scholl, Stuttgart, Germany, assignorto Robert Bosch GmbH. Stuttgart, Germany, a limited-liability company ofGermany Filed Aug. 17, 1967, Ser. No. 661,339 Claims priority,application ligrmany, Aug. 31, 1966,

B 8 Int. Cl. F02m 51 H03k 3/295 U.S. Cl. 123-32 5 Claims ABSTRACT OF THEDISCLOSURE The present invention relates to an impulse generator, inwhich the time duration of the pulses is widely variable, and includinga multivibrator circuit.

It is often desirable to change the time duration of pulses generated ina multivibrator over a wide range. Known arrangements utilizeinter-stage coupling, including a R-C network, thus changing the timeconstant by change of the resistance or the capacity; it has also beenproposed to change the inductance in multivibrator circuits in which thecoupling is an inductive-resistance coupling, or the resistance of sucha L-R network.

Multivibrator circuits which are to operate under difiicult conditions,such as in the machine area of a factory, in rolling mills, motorvehicle or the like, must have a sturdy adjustment element to change theimpulse frequency, an element which is not subject to wear and tear,even under constant change. Inductive elements are much better suited tochange, then resistance potentiometers, since movement of an iron core,or of a coil, can be caused with substantially no wear, or maintenancerequirements. Even quality potentiometers are subject to a certainamount of wear and further, potentiometers are ordinarily quitesensitive to vibration.

Inductive adjustment members, in which the inductive value changes withmotion of an adjustable element, are comparatively expensive. This isparticularly true if, in mass production, a large number of suchinductive elements are to be built having identical characteristics, forexample, for use with a fuel injection arrangement for motor vehicles,in which the adjustable element of an inductive coupling unit is movablein dependence on the vacuum in the intake manifold of the internalcombustion engine. Final adjustment and alignment of such inductiveelements is required, such adjustment being costly and time-consuming.

Inductive coupling elements, when used for low frequencies, as is thecase in gasoline injection systems for gasoline engines, cause furtherproblems. The iron core must be of substantial mass, so that the lowerlimiting frequency is sufiiciently low. This further increases the priceof such coupling elements, and increases their size so that inductiveelements are often much larger than the remainder of circuit componentswith which they are used, particularly when printed circuits orintegrated circuit elements are used therewith.

It is an object of the present invention to provide an impulsegenerator, utilizing an inductive coupling eleatent C 3,464,396 PatentedSept. 2, 1969 ment in which the aforementioned disadvantages areavoided. More particularly, the impulse generator of the presentinvention, utilizing an inductive coupling element, to adjust the timeduration of impulses should be so designed that the inductivity of thiscoupling element has no essenial influence on the time duration of theimpulses themselves, and which does not place high requirements on thelower limiting frequency thereof.

Subject matter of the present invention Briefly, in accordance with thepresent invention, a multivibrator circuit has a differentialtransformer coupled to the output thereof, the differential transformerhaving an adjustable core element so that the coupling to the secondarycan be varied. An electronic, voltage-sensitive switch, having apredetermined threshold is connected to the output of the differentialtransformer over a charging condenser. The switching state of thevoltage-sensitive switch is then determined by the potental on thecondenser.

The dilferential transformer thus has a couple only a sort, square wavepulse, generated by the multivibrator, which charges the condenser to acertain value. The wave shape of this pulse, transmitted by thedifferential trans former, has very little influence on the pulseduration, so that the steepness of the flanks, both on the rising aswell as on the falling side, is not critical.

The threshold voltage-sensitive switch then causes a stretching out ofthe impulse duration by a predetermined factor, so that when themultivibrator supplies an impulse of duration t,, the impulse durationat the output of the voltage-sensitive switch will be a xt The lowerlimiting frequency of the differential transformer is thus determined byt and not by the much longer time period of the pulses at the output ofthe voltage-sensitive switch, and the differential transformer can thusbe constructed in simpler, and hence cheaper, form.

The output signal of the differential transformer may be applied to thecondenser over a rectifier and thus the charging time constant of thecondenser will become independent of its discharge time.

The structure, organization, and operation of the invention will now bedescribed more specifically with reference to the accompanying drawings,wherein:

FIG. 1 is a circuit in accordance with the present invention, applied toan internal combustion engine;

FIG. 2 is a longitudinal section through a differential transformeralong line IIII of FIG. 3;

FIG. 3 is a front view of the differential transformer in accordancewith FIG. 2; and

FIG. 4 is a series of graphs of voltage (ordinate) versus time(abscissa) illustrating the operation of the circuit of FIG. 1.

Referring now to the drawings, and more particularly to FIG. 1:

A monostable multivibrator 10, including a pair of pnp transistors 11and 12 has its output connected to a differential transformer 13. Theoutput of the differential transformer 13 is applied over a diode 14 toa condenser 15; and then through a coupling resistance 48 to avoltagesensitive switch 16, having a lower threshold value. Switch 16 isin the form of a Schmitt trigger, the switching state of which dependson the potential on condenser 15; switch 16 contains two pnp transistors17 and 18.

The monostable multivibrator 10 is conventional. The base of transistor11 has, over a condenser 21, positive pulses schematically indicated at22 applied thereto; pulses 22 are obtained from an impulse generator IG,associated with the shaft S of an internal combustion engine E. Thepulses thus are synchronized with the speed of the engine. Theconnections are schematically indicated by dashed lines and the impulsegenerator may be of any well known 3 type, such as a cam cyclicallyclosing a switch, a magnetic element passing a coil, photoelectric meansor the like. The base of transistor 11 is further connected over aresistance 23 to a negative bus 24 of a source of power; the emitter isconnected to positive bus 25. The potential between lines 24, 25 may be,for example, 12 v.

A condenser 26 connects the base of transistor 11 to the collector oftransistor 12. The collector of transistors 11 and 12, each, isconnected over a collector resistance 27, 28, respectively with negativeline 24; further, the collector of transistor 11 is connected directlyto the base of transistor 12, the emitter of which connects directly topositive bus 25.

In operation of the multivibrator 10, transistor 11 is usuallyconductive and transistor 12 is blocked, if no positive pulse 22 issupplied. As soon as a positive pulse 22 is applied to the base oftransistor 11, this transistor will block, its collector will becomestrongly negative, and the base of transistor 12 will thus likewisebecome negative. Transistor 12 will become conductive. The collectorpotential will then shift in a positive direction. Condenser 26retransmits this potential jump to the base of transistor 11 and retainsit positive. Only when condenser 26 has sufliciently discharged overresistance 23, then transistor 11 after an impulse period indicated inFIG. 4 with t, will again become conductive, causing transistor 12 toblock.

Differential transformer 13 is connected to the output of multivibrator10. It has two primary windings 35, 36; the windings 35, 36 are inparallel with the collector resistance 28 of transistor 12. A secondary37 of transformer 13 has one terminal connected to positive bus 25, theother to the cathode of a diode 14; the anode of diode 14 connects toone electrode of condenser 15, the other side of which is againconnected to positive bus 25.

Differential transformer 13 has a movable element indicated as movablecore element 38. It is connected by means of a linkage 39 with apressure sensing element 40 connected to the intake manifold of engineE, in wellknown manner. Pressure sensing element 40, may, for example,be a vacuum chamber with a diaphragm. The intake manifold has a vacuumtherein which depends on the position of the throttle of the engine; ifthe throttle is closed, the vacuum is high, and link 39 is shiftedupwardly in the direction of arrow 41. If the throttle is open, there islittle, or hardly any vacuum in the intake manifold, and linkage 39moves against the direction of arrow 41, that is downwardly in FIG. 1.With motion of linkage 39, the iron core 38 shifts accordingly.

FIGS. 2 and 3 illustrate one form of a differential transformer 13,generally containing a rectangular frame 43 having a pair of bores inwhich a brass tube 44 is secured. A pair of coil formers 46, 47,separated by a center part of ferro-magnetic material 45, are arrangedupon the brass tube 44. l

Coil 46 has an inner winding forming the primary 35, and an outerwinding forming one half of secondary 37; coil 47 contains an innerwinding forming the primary 36 and an outer winding forming the secondhalf of secondary 37. The direction of winding of the separate coils isindicated in conventional form by a point or a cross, respectively. Asclearly appears from FIG. 2, the two primaries 35, 36 are wound inopposite sense whereas the two halves of the secondary 37 have the samesense of winding. This is further indicated by the dots in FIG. 1.

When movable core 38, within the brass tube 44, is in its centerposition, indicated with dashed lines, then the coupling between the twoprimary windings 35 and 36 with the secondary 37 is symmetrical. Analternating current potential applied to the primaries will thus inducein the secondary equal and opposite potentials which cancel each other.If core 38 is shifted from its center position to the full line positionof FIG. 2, then the windings on coil 47 are coupled more tightly thanthose of coil 46 and a potential will appear at secondary 37. The inputinductivity of the dilferential transformer 13 has only a negligibleinfluence on the amplitude of this secondary potential.

FIG. 4 illustrates, in the upper row, the output impulses ofmultivibrator 10; the second row from above indicates the potential 11at the output of differential transformer 13 for various positions ofiron core 38. With a high vacuum, the potential will be that shown underthe column (a), that is when the core 38 is practically in its centerposition; the column (b) indicates the potentials with somecut-of-center position of core 38; and under (c) a potential withsubstantial out-of-center position is indicated. As seen, the potentiala increases as the out-ofcenter position of core 38 increases.

The potential u is supplied over diode 14 to condenser 15 to charge thecondenser to a predetermined potential. After the termination of theimpulse, the condenser discharges over a pair of serially connectedresistances 48, 49, in parallel therewith. Condenser 15 thus will have apotential thereacross as seen in the third row of FIG. 4, that is u (t)indicated for the three cases (a), (b), (c).

The base of transistor 17 of the threshold switch 16 is connected to thejunction or tap points of resistances 48, 49. Its collector is connectedover a collector resistance 52 with a negative line 24, and over acoupling resistance 53 with a base of transistor 18, which, in turn, isconnected over a resistance 54 to the positive bus 25.

The emitters of transistors 17, 18, respectively, is connected together,and over a common emitter resistance, 55 to positive line 25. Thecollector of transistor 18 connects over a collector resistance 56 withnegative bus 24. Further, between the collector and resistance 56, aload, generally indicated at 57, is connected which may, for example, bean electromagnetic fuel injection unit of a gasoline injection systemfor engine E.

When the potential 1 on the condenser 15 is zero, transistor 17 isblocked and transistor 18 conductive, since it has a negative potentialon its base, applied by the resistances 53, 54, forming a voltagedivider. If condenser 15 charges, its anode, connected to the diode 14,will become negative with respect to the positive line 25. When acertain, predetermined negative potential is reached, which is indicatedin FIG. 4 with w and which is the threshold potential, transistor 17becomes conductive and transistor 18 blocks. This condition persistsuntil the condenser 15 is discharged so that the potential of the baseof transistor 17 drops below the threshold potential ofvoltage-sensitive switch 16. Switch 16 returns to its quiescent state,that is, transistor 17 becomes blocked and transistor 18 conductive.

The time between the switchover of the threshold switch 16 depends onthe charge applied to the condenser 15. Thus, the time duration ofpulses 11., applied to the load 57 will depend on the position of ironcore 38 of the differential transformer 13, as indicated in FIG. 4 inthe lowest horizontal row. When iron core 38 is almost in its centerposition, that is, column (a), pulse 11 will be short. As the iron core38 moves out of the center position, pulses in; become longer, asillustrated in the columns under (b) and (c). It has been found that theimpulse duration t, of the multivibrator 10 can be changed in a range offrom 1:10.

The circuit here described enables adaptation to a number of engineswith difierent characteristics, and provides ready change of theduration of the pulses 11 For example, resistances 48 and/or 49 can bechanged to change the threshold potential u either by raising orlowering it; the impulse duration 1, of the multivibrator 10 can bechanged in a known manner; rather than having a single condenser 15, acondenser network with switches can be used. Thus, the application ofthe invention can be adapted to widely varying requirements which arenot limited to the application for a gasoline injection system for amotor vehicle, but also can be applied for ignition systems for motorvehicles, to control electromagnetic clutches and many other devices.

What is claimed is:

1. An impulse generator providing impulses of widely varying timeduration comprising a multivibrator circuit a differential transformer(13) of adjustable inductivity, said difierential transformer beingcoupled to the output of said multivibrator circuit; an electronicthreshold voltage sensitive switch (16); and a charging condenser saidcharging condenser interconnecting the output of said differentialtransformer and said threshold voltage-sensitive switch, the switchingstate of said switch being determined by the potential (u across thecondenser.

2. Impulse generator as claimed in claim 1 including a rectifier (14)interconnecting the output of the differential transformer (13) and saidcondenser (15).

3. Impulse generator as claimed in claim 1 wherein said multivibrator(10) is a monostable multivibrator, adapted to be connected to a sourceof trigger pulses (22).

4. Impulse generator as claimed in claim 3 in combination with aninternal combustion engine (B), said trigger impulses being synchronizedin time with the rotation of the output shaft (S) of said engine; theadjustable differential transformer being provided with an adjustableelement (38) adjustably coupling the primary and secondary coils of saidtransformer; and means adjustably interconnecting the adjustableelements of said transformer with said engine so that the position ofsaid adjustable element within the transformer is dependent upon anoperating parameter of the engine, whereby the switching points, intime, of said threshold voltage-sensitive switch (16) will be a functionof speed of the engine and of the respective operating parameter.

5. Impulse generator as claimed in claim 4 wherein said engine has amanifold vacuum transmitter and said interconnection means are coupledto the core elements of said transformer, and said vacuum transmitter,so that, with increasing vacuum, said interconnection means causeadjustment of said core element in a direction which decreases theswitching times of said threshold voltagesensitive switch (16) uponcharging and discharging of said condenser.

References Cited UNITED STATES PATENTS 3,005,447 10/ 1961 Baumann et a1.3,338,221 8/ 1967 Scholl.

LAURENCE M. GOODRIDGE, Primary Examiner US. Cl. X.R. 123-119, 139

